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[InstCombine] Rewrite multi-use GEPs when simplifying comparison (#146100)

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We already do this when both sides are a GEP, but not if only one is.
This ensures that the offset arithmetic is not duplicated.
This commit is contained in:
Nikita Popov
2025-07-01 14:26:47 +02:00
committed by GitHub
parent 9b13dfdfbc
commit b8b7494551
3 changed files with 31 additions and 2 deletions
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2
llvm/lib/Transforms/InstCombine/InstCombineCompares.cpp
View File

@@ -711,7 +711,7 @@ Instruction *InstCombinerImpl::foldGEPICmp(GEPOperator *GEPLHS, Value *RHS,
Value *PtrBase = GEPLHS->getOperand(0);
if (PtrBase == RHS && CanFold(GEPLHS->getNoWrapFlags())) {
// ((gep Ptr, OFFSET) cmp Ptr) ---> (OFFSET cmp 0).
Value *Offset = EmitGEPOffset(GEPLHS);
Value *Offset = EmitGEPOffset(GEPLHS, /*RewriteGEP=*/true);
return NewICmp(GEPLHS->getNoWrapFlags(), Offset,
Constant::getNullValue(Offset->getType()));
}

28
llvm/test/Transforms/InstCombine/icmp-gep.ll
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@@ -221,6 +221,34 @@ define i1 @eq_base_inbounds_commute_use(i64 %y) {
ret i1 %r
}
define i1 @ne_base_inbounds_use_scaled(ptr %x, i64 %y) {
; CHECK-LABEL: @ne_base_inbounds_use_scaled(
; CHECK-NEXT: [[G_IDX:%.*]] = shl nsw i64 [[Y:%.*]], 3
; CHECK-NEXT: [[G:%.*]] = getelementptr inbounds i8, ptr [[X:%.*]], i64 [[G_IDX]]
; CHECK-NEXT: call void @use(ptr [[G]])
; CHECK-NEXT: [[R:%.*]] = icmp ne i64 [[Y]], 0
; CHECK-NEXT: ret i1 [[R]]
;
%g = getelementptr inbounds i64, ptr %x, i64 %y
call void @use(ptr %g)
%r = icmp ne ptr %g, %x
ret i1 %r
}
define i1 @ne_base_use_scaled(ptr %x, i64 %y) {
; CHECK-LABEL: @ne_base_use_scaled(
; CHECK-NEXT: [[G_IDX_MASK:%.*]] = shl i64 [[Y:%.*]], 3
; CHECK-NEXT: [[G:%.*]] = getelementptr i8, ptr [[X:%.*]], i64 [[G_IDX_MASK]]
; CHECK-NEXT: call void @use(ptr [[G]])
; CHECK-NEXT: [[R:%.*]] = icmp ne i64 [[G_IDX_MASK]], 0
; CHECK-NEXT: ret i1 [[R]]
;
%g = getelementptr i64, ptr %x, i64 %y
call void @use(ptr %g)
%r = icmp ne ptr %g, %x
ret i1 %r
}
define i1 @eq_bitcast_base(ptr %p, i64 %x) {
; CHECK-LABEL: @eq_bitcast_base(
; CHECK-NEXT: [[GEP_IDX_MASK:%.*]] = and i64 [[X:%.*]], 9223372036854775807

3
llvm/test/Transforms/PhaseOrdering/loop-access-checks.ll
View File

@@ -24,7 +24,8 @@ define void @test_fill_with_foreach([2 x i64] %elems.coerce) {
; CHECK-NEXT: [[ELEMS_COERCE_FCA_0_EXTRACT:%.*]] = extractvalue [2 x i64] [[ELEMS_COERCE]], 0
; CHECK-NEXT: [[TMP0:%.*]] = inttoptr i64 [[ELEMS_COERCE_FCA_0_EXTRACT]] to ptr
; CHECK-NEXT: [[ELEMS_COERCE_FCA_1_EXTRACT:%.*]] = extractvalue [2 x i64] [[ELEMS_COERCE]], 1
; CHECK-NEXT: [[ADD_PTR_I:%.*]] = getelementptr inbounds i32, ptr [[TMP0]], i64 [[ELEMS_COERCE_FCA_1_EXTRACT]]
; CHECK-NEXT: [[ADD_PTR_I_IDX:%.*]] = shl nsw i64 [[ELEMS_COERCE_FCA_1_EXTRACT]], 2
; CHECK-NEXT: [[ADD_PTR_I:%.*]] = getelementptr inbounds i8, ptr [[TMP0]], i64 [[ADD_PTR_I_IDX]]
; CHECK-NEXT: [[CMP_NOT_I_I_I_I:%.*]] = icmp slt i64 [[ELEMS_COERCE_FCA_1_EXTRACT]], 0
; CHECK-NEXT: br i1 [[CMP_NOT_I_I_I_I]], label [[ERROR:%.*]], label [[FOR_COND_PREHEADER_SPLIT:%.*]]
; CHECK: for.cond.preheader.split: